1. Field of the Invention
The invention relates to a data communication system of a type comprising a plurality of data stations which are interconnected by a common communication medium, each data station comprising a data transmitter for transmitting a data signal via the communication medium and further comprising a data receiver for receiving a signal transmitted by one of the other data stations via the communication medium and each data station comprising arbitration means to prevent more than one data transmitter transmitting simultaneously over the communication medium.
2. Description of the Prior Art
A system of the above type is known from the article: "Improvements of the multiprocessing capabilities of microprocessor busses", by W. Mahr and R. Patzelt, published in Euromicro Journal 4 (1978), pages 207-219; and is suitable for use in computer systems and as communication systems in, for example, hotels, hospitals, factories, offices and ships.
So, generally, the data stations are provided in spatially different locations within a limited area. In systems of this type the information is usually transmitted in successive packets. As there is potentially more than one (prospective) user simultaneously, while only one communication medium is available for one user at a time, a provision is required with which it is possible to determine which data station (user) is authorized to transmit the next packet. In para. 3.4 of the above-mentioned article this provision, which is commonly referred to as an arbitration provision, is implemented such that each data station is given a priority code word. The data stations which simultaneously request access to the communication medium offer this code word simultaneously to an arbitration bus interconnecting the data stations. The data station having the highest (priority) code word is given access to the communication medium while all the other stations are rejected. The code word is binary coded. In a number of steps, namely by first comparing the most significant bits of each code word and thereafter sequentially the less significant bits one data station is ultimately selected. A disadvantage of this manner of arbitration is that the system comprises an additional bus, known as the arbitration bus, which is connected to all data stations.